The present invention relates to an optical reproduction system. Optical reproduction systems which reproduce an object on an image plane parallel to the plane of the object and where the image produced in the image plane is rotated by 90.degree. relative to the object are known to the prior art in numerous designs. Examples are the so-called Dove/Amici prisms, the Abbe/Konig prism, and the Schmidt/Pechan prism. These reproduction systems differ among themselves significantly in the number of reflecting surfaces they employ (Dove/Amici: 1, Abbe/Konig : 3, Schmidt/Pechan: 5). But each of them has an odd number of reflecting surfaces, with the result that the produced image is indeed rotated 90.degree. on the image plane relative to the object; in each case, however, the image is also inverted in its orientation (a right-handed system becomes a left-handed system, and vice versa).
Of interest are those reproduction systems which rotate the object 90.degree. and are used in photographic copy machines and photographic processing paths. In the production of copies out of originals, for example from the negatives of a negative film, there are both film frames in full format (full-frame, for example, 24 mm.times.36 mm) and film frames in half-format (half-frame, for example, 24 mm.times.18 mm). On the negative film the half-frames are rotated 90.degree. relative to the full-frames due to the uniform film width. In the case of conventional simple exposure on paper, the copied image of the half-frame original would also be rotated by 90.degree. on the paper relative to the image of a full-frame original.
As a rule, films with originals (film frames) in full-frame arise more frequently than films with half-frames that are rotated 90.degree.. Still, films with rotated half-frames are so commonplace today and arise in such large number that for an efficient distribution of load on copy machines or photographic processing paths it must be possible to copy onto the paper the half-frame originals rotated 90.degree., and in such a way the copies of these half-frame originals rotated 90.degree. have the same position and also the same dimensions on the paper as the copies of full-frame originals.
This requirement quickly becomes obvious: whether the client has shot a film with half-frame or full-frame originals, he will want to receive paper copies, for example, in the particularly popular 9 cm.times.13 cm format. At the same time, copying with copy machines usually involves first combining the individual films or film strips to form a long tape. This long tape is then processed by exposure onto the paper. Likewise a long tape of photosensitive paper is employed for copies of one and the same format. This long paper tape has a uniform width (always for copies of one and the same format). If an attempt were made to copy both the originals in full-frame and the half-frame originals rotated 90.degree. onto the paper with a single enlargement, the paper width-adjusted to the smaller dimension (for example, 9 cm dimension) of the copies of full-frame originals--would be insufficient for the copies of half-frame originals. Even if the paper width were given adequate dimensions (which for copies of full-frame originals would result in a large excess length on the paper margin), the paper tape would have to be advanced each time a non-uniform distance before the next copy could be cut from the paper tape, depending on whether the next copy on the paper tape was that of a full-frame or a half-frame original inasmuch as the copy of the half-frame original would be copied onto the paper rotated in 90.degree. rotation.
In the past, therefore, copy machines were proposed in which--in the case of half-frame originals rotated 90.degree. --these rotated originals were copied onto the paper in 90.degree. "reverse rotation", and such copies consequently occupy the same position on the paper as copies of full-frame originals that have not been rotated in copying. To be sure, the reproduction systems discussed at the outset are unsuited for this purpose, since--as already mentioned--they have an uneven number of reflecting surfaces, and though they could provide the 90.degree. rotation, the orientation of the objects shown on the originals would be inverted. On the other hand, an even number of reflecting surfaces, which can also provide the 90.degree. rotation, will maintain the orientation of the reproduced objects. Copy machines which have these even number of reflecting surfaces are described in, for example, U.S. Pat. No. 4,743,103 and EP 0,157,325.
The solution described in U.S. Pat. No. 4,743,103, employing two Schmidt/Pechan prisms and a large number of lenses, is disadvantageous in several respects. It is disadvantageous with respect to spatial requirements (a reproduction system for use in copy machines cannot be of any desired size). Primarily, however, the expense with respect to the high precision required for justification of the reflecting surfaces of the prisms with the increasing number of reflections (in the present example the number of reflections is ten) is very high, and a true reproduction of the original by the produced copy is associated with a very high cost--or will otherwise be considerably impaired by a less precise justification of the prisms and their reflecting surfaces.
The variation suggested in EP 0,157,325 comprises a total of six reflecting surfaces, four of which are required to achieve the desired 90.degree. rotation. To be sure, after four reflections the incoming optical axis and the outgoing optical axis of the system would not coincide and the image would consequently be copied in displaced fashion on the paper. Such displacement results in increased paper consumption, since the gaps in the paper tape between copies which are produced from half-frame originals and copies which are produced from full-frame originals are larger than when only copies of full-frame originals are produced. In addition, displacement produces increased expense in terms of the transport means and the cutting device of the corresponding copy machine or photographic processing path: the paper tape must be advanced a differing distance before the next copy can be cut from the paper tape, depending on whether a copy of a full-frame or a half-frame original is the next copy on the paper tape. In order to avoid this kind of displacement and the associated expense, EP 0,157,325 furnishes two additional reflecting surfaces which assure that the image rotated 90.degree. is not copied in displaced fashion but rather in the same position on the paper as the unrotated image of a full-frame original. Additional reflecting surfaces, however, make for an increased spatial requirement, apart from the increased expense represented by the additional mirrors. Most important, however, the expense with respect to the high precision required in justifying the prisms and their reflecting surfaces remains very high, so that a true reproduction of the original by the produced copy can only be achieved at great expense, or at the cost of reduced quality when there is a less precise justification of the prisms and their reflecting surfaces.